Conventional power supplies known to the art typically employ two methods of recovery during a power failure. For a short input power failure (typically less than 20 milliseconds), large capacitors may be utilized with a converter to supplement input power. When an input power supply is interrupted for a period of greater than 20 milliseconds, uninterruptable power supply (UPS) equipment external to the power supply is necessary.
When large capacitors are utilized to supplement input power for short power failures, a large inrush current is produced when input power is regained. This requires additional circuitry, typically an inrush current limiting resistor and a relay or transistor with control circuitry, to accommodate the inrush current which adds cost to the power supply. The incorporation of UPS equipment with a power supply also adds cost to the power supply. Consequently, a method and system of supplementing input power during a power failure that may not produce an inrush current is necessary.